So I'm going to detach my heated bed wiring (the heater,

3D Printing
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So I’m going to detach my heated bed wiring (the heater, not the thermistor) from my Melzi board and power it via external ATX power supply…

How do people hook this setup up? I assume the heater circuit gets switched by a relay? Or a transistor? Or something else?

And, how much power can I get on a single “molex” cable? I’m think the RRP heated bed is 150 watt (not entirely sure) - will the wiring from the ATX be able to handle that on one cable?

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Look for a Solid State Relay (SSR). Make sure to choose one that has the right input voltage range (from the Melzi) and the right load voltage range (eg: can run 12VDC output, not the ones for 100-300VAC).

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I am using a mossfet on a separate board. All the POS wires go direct to the heatbed and the NEG wires are switched through the fet.

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Cheers guys :wink: making a trip to Jaycar after work :wink: :wink:

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I’m curious. Why not power the Melzi from the ATX supply and use the built in MOSFET?

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I’m guessing that the heated bed is drawing too much current.

While the MOSFET itself might handle the current, the PCB tracks, the connectors and any fuses might not.

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Yeah kinda… or rather, It was never getting hot enough… AND the connection to the board is (IMHO) very poor being only screw-clamped (I think RepRapPro over-shoot with the thickness of the power and heat-bed wires… AND they suggest tinning them AND attaching the heat-sink fan (for the hot end) to the power inlet… there’s a LOT of copper in those 2 lots of screw terminals… I just desoldered and replaced the power connector last night (cos it shorted or… something, “died”…) and removed the heat-bed connector and now I think I’ll beef it up with the ATX supply - then I can also have a 12v switchboard for additional fans / lighting etc too…

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@Wayne_Friedt - I went to the local electronics shop (they never EVER have anything I want).

I’ve decided to go down the mosfet road because they didn’t have and won’t get the relay I need for this (and WOW - one that was close was very expensive!).

So may I ask more specifically what your setup is? I’ve done a project using TIP 31 transistors - is a mosfet similar to wire up? And what spec / part number is yours? Do I just need the mosfet or other components in that setup?

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@Jarred_Baines Ya sure glad to help. i am using a BUZ11, which is not the best choice but i had one so that’s that. A better choice would be a IRLB8743PBF and the RS # is 725-9325.

The setup: https://plus.google.com/u/0/+WayneFriedt/posts?cfem=1

I used an opto-isolator also again because i have them but it can be omitted.
Really you are controlling the NEG on the heatbed. The POS get wired direct.

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Hey guys, I haven’t had time to hook anything up, been mega busy! but I was wondering - is a automotive “horn relay” any good for this purpose? I can’t find any info as to why it wouldn’t do the job… Anyone know?

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A horn relay could work if using " bang bang " heating. If using PID i would say not. Just switching to fast for the relay. Either way i would use a SSR instead.

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What if…
I HAVE a horn relay…
and I’ve only found SSR’s for $50 locally…

Could I - use the horn relay without burning my house down (given it has a high enough rating) and - purchase an SSR off ebay and wait for it to come? lol :slight_smile:

I’m itching to print some ABS parts for my ingentis build, but - no HBP!

It is definitely bang-bang with my board / firmware :wink:

Thanks for helping guys :wink:

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It will work until it fails, ha

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Which will be an open-circuit type fail and non harmful?

I might just wait anyways :slight_smile: lol

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Right power to energize. No power off.